About half of all common colds, one of the most frequent infections of humans, are caused by the human rhinoviruses. These viruses are members of the Picornaviridae, a family composed of small, non-enveloped positive strand RNA viruses. The pathogenesis of rhinovirus infection is poorly understood because the viruses replicate only in higher primates. A mouse model for rhinovirus infection would provide information about rhinovirus pathogenesis and stimulate the identification of antiviral and anti-inflammatory drugs. We propose to isolate rhinovirus variants that can replicate in mouse cells, identify mutations responsible for the change in host range, and study the mechanism of action of these mutations. Mouse-adapted rhinoviruses will be used to infect transgenic mice expressing human ICAM-1, the cellular receptor for major group human rhinoviruses. Two specific aims are proposed. Aim 1: Determine the molecular basis of rhinovirus host range. Rhinovirus type 16 has been found to replicate in mouse cells expressing the viral receptor, human ICAM-1, and a viral variant was selected that replicates more efficiently in these cells and causes extensive cell death. The mutations that confer this host range phenotype are located in viral nonstructural polypeptides 2B and 2C. Experiments are designed to determine how these mutations influence viral replication, by determining their effect on viral RNA and protein synthesis, and their effects on the host cell membranes. Host cell proteins that interact with 2B and 2C will be identified to determine the mechanism of action of the host range mutations. Aim 2: Develop a transgenic mouse model for rhinovirus infection. Transgenic mice that express human ICAM-1 in the respiratory tract will be developed. Human ICAM-1 transgenic mice will be infected with rhinovirus type 16 and rhinovirus type 16 adapted to mouse cells expressing human ICAM-1 to study the pathogenesis of rhinovirus infection, including the sites of virus replication within the respiratory tract, the extent of cell damage in the host, the nature of the immune response, and the role of the immune response in pathogenesis.